1. Field of the Invention
The invention concerns a 3D milling machine and a 3D milling process.
2. Description of the Related Art
A 3D milling machine includes milling unit with a motor driven spindle for receiving a milling tool, a work table for clamping or setting work pieces, and guide elements and drive means for producing relative movement of the milling unit and the work table in three spatial directions. From DE 199 10 880 A1 such a milling machine is known, which additionally includes a laser device for emitting a laser beam, which makes possible a processing of the work piece via the laser beam as an alternative to the milling process.
Special materials such as for example ceramic or certain types of steel are preferably milled with laser assistance. Therein the laser beam locally heats the work piece, in order to bring the cutting zone to a temperature at which the material is more easily removed by cutting or turning, in particular with higher cutting speeds. Various processes for laser-assisted milling are described in U.S. Pat. No. 5,906,459.
Free form surfaces are normally milled using a spherical cutter, as described for example in DE 39 22 463 A1. With hard special materials a milling of free form surfaces is however not possible, only diamond cutting, wherein however the metal removal by cutting is of very small volume.
The invention makes possible a milling process of free form surfaces with laser assistance.
In the processing of free form surfaces using a spherical cutter, changes in direction continuously occur. Since the laser device is so positioned in the inventive milling machine, that it can carry out a precise movement about a point on the beam axis, in which the spherical cutter is located, one can achieve with a simple mechanical movement of the laser device, that the laser xe2x80x9cburn spotxe2x80x9d (heated area) precedes the spherical cutter mill by a certain lead separation, in order to heat the entire cross-section being removed by metal cutting. During a change in direction the laser burn spot follows a part of a circle or elliptical track about the spherical cutter. Therein the rotatable or, as the case may be, pivotable work table makes it possible to keep constant the angle of incidence of the spherical cutter to the work piece outer surface at the actual processing point, in at least one plane, such that optimal engagement conditions always exist at the milling cutting site and therewith a large-as-possible rate of advance can be selected.
Preferably, the laser device is mounted cardanically at a point along the beam axis, that is, in a rotatable U-mount or hanger, and mounted eccentrically at a point on the beam axis at a distance therefrom, in particular in an eccentric subassembly, which makes possible an adjustment of the amplitude of the precise movement.
The laser device is preferably mounted to the milling spindle head with which the work spindle is associated. An adjustable mounting makes possible a rapid adaptation to various miller lengths and miller diameters.
A suitable light source could in principle be integrated in the laser device, however in a preferred embodiment a separate light source is envisioned, which is connected with a laser emitter or optic via a flexible light guide, thereby forming the moveable laser device of the milling machine.
Since the laser beam should not be permitted to rest upon the spherical cutter, the movement of the laser burn spot is limited to a semi-circle or, as the case may be, half ellipse about the spherical cutter essentially (based upon the angle between the laser beam axis and axis of the work spindle the laser burn spot on the construction component as a rule does not follow a semi-circle, but rather an elliptical track). Thus initially a key milling line should be carried out as milling type or strategy, in which the direction of milling does not change more than 180xc2x0. Within certain limitations, other milling strategies are also possible.